Photoelectric conversion device and manufacturing method of the photoelectric conversion device

ABSTRACT

A manufacturing method includes a first process for forming a first gate electrode for a first MOS transistor and a second gate electrode for a second MOS transistor on a substrate including a semiconductor region defined by an insulator region for element isolation, a second process for masking a portion located above the semiconductor region of the first gate electrode to introduce an impurity to a source-drain region of the first MOS transistor, and a third process for forming a first conductor member being in contact with the portion of the first gate electrode through a first hole disposed on an insulator member covering the substrate and a second conductor member being in contact with the second gate electrode through a second hole disposed on the insulator member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present technique relates to a photoelectric conversion deviceincluding a metal oxide semiconductor (MOS) transistor.

2. Description of the Related Art

In a photoelectric conversion device, such as an image sensor, millionsto tens of millions of pixel circuits are arranged, and a signal fromthe pixel circuit may be used as a pixel signal. Expansion of an area ofa light receiving region of a photoelectric conversion element iseffective to improve a sensitivity and a saturated electron amount ofthe photoelectric conversion element. In order to expand the area of thelight receiving region of the photoelectric conversion element, it isnecessary to reduce an area other than the light receiving region of thepixel circuit.

In a paragraph 0025 of Japanese Patent Application Laid-Open No.2013-84740, it is described that a first contact plug (321) connected toa transfer gate electrode (121) is arranged on a first active portion(2A) such as on a channel region.

In miniaturization and a layout change of devices in the pixel circuit,there are restrictions in manufacturing processes of the photoelectricconversion device and in characteristics of an MOS transistor in thepixel circuit. When a contact plug is arranged on a channel region as inthe case of Japanese Patent Application Laid-Open No. 2013-84740, thereis a possibility of deteriorating characteristics of a transistor. Thepresent technique is directed to improvement in performance of a pixelcircuit.

SUMMARY OF THE INVENTION

According to an aspect of means of solving the above-described issue, amanufacturing method of a photoelectric conversion device in which apixel circuit including a metal oxide semiconductor (MOS) transistor isarranged, the manufacturing method includes a first process for forminga gate electrode and a source-drain region of the MOS transistor, asecond process for masking a first portion in the gate electrode, thefirst portion being constituted by polysilicon and located above achannel region of the MOS transistor, and introducing an impurity havinga conductivity type same as that of the source-drain region to a secondportion located in the source-drain region, and a third process forforming a conductor member being in contact with the first portionthrough a first hole disposed on an insulator member covering the MOStransistor and a conductor member being in contact with the secondportion through a second hole disposed on the insulator member.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a photoelectric conversiondevice.

FIGS. 2A to 2C are schematic diagrams illustrating pixel circuitsaccording to a first exemplary embodiment.

FIGS. 3A to 3D are schematic diagrams illustrating a manufacturingmethod of the photoelectric conversion device.

FIGS. 4A to 4C are schematic diagrams illustrating pixel circuitsaccording to a second exemplary embodiment.

FIGS. 5A to 5D are schematic diagrams illustrating the manufacturingmethod of the photoelectric conversion device.

DESCRIPTION OF THE EMBODIMENTS

Various exemplary embodiments will be described below with reference tothe attached drawings. The common reference numerals are used for thecommon configurations throughout a plurality of the drawings in thefollowing descriptions and drawings. Therefore, the commonconfigurations are described by mutually referring to the plurality ofthe drawings, and the descriptions of the configurations with the commonreference numerals are properly omitted.

First, an outline of a configuration of a photoelectric conversiondevice is described which is common to a plurality of exemplaryembodiments.

FIG. 1 illustrates an example of a circuit configuration of aphotoelectric conversion device 1. The photoelectric conversion device 1can include a pixel unit 18, a driving unit 24, a signal processing unit25, a control unit 27, and an output unit 29. The pixel unit 18 includesa plurality of pixel circuits 2 which are arranged to constitute aplurality of rows and a plurality of columns. The pixel circuit 2includes at lease a photoelectric conversion element and a plurality ofMOS transistors for generating a signal from a charge generated by thephotoelectric conversion element. In FIG. 1, a configuration in whichthe pixel circuits 2 are arranged in three rows by four columns isillustrated to facilitate understanding. The plurality of pixel circuits2 of the pixel unit 18 is connected to the driving unit 24 by a powersource line 19 and signal lines 20, 21, and 22 and also connected to thesignal processing unit 25 by an output signal line 23.

The driving unit 24 includes, for example, a shift register and outputsa driving signal to the pixel unit 18 according to a clock signal todrive each pixel circuit 2 by row. The signal processing unit 25 isdisposed corresponding to each column and reads a signal by column fromeach pixel circuit 2 output in response to the above-described drivingsignal. Each signal read by the signal processing unit 25 ishorizontally transferred via transfer units 28 a and 28 b according to acontrol signal from the control unit 27 and sequentially output from theoutput unit 29 by column.

The signal processing unit 25 can perform processing on a signal fromthe pixel circuit 2 by a circuit configuration according to, forexample, a correlated double sampling (CDS) method. The signal processedby the signal processing unit 25 is amplified by the output unit 29 andcan be output as a signal. The signal processing unit 25 can include anamplifier circuit and an analog-to-digital (AD) conversion circuit aswell.

The photoelectric conversion device 1 can further include a package forhousing a semiconductor substrate. The package can include a base bodyto which a chip including the above-described pixel unit 18 and othersare fixed, a lid body facing the chip, and a connection member, such asa wire bonding and a lead frame enabling exchange of signals between thechip and the outside.

The photoelectric conversion device 1 is configured as at least one ofan imaging device (an image sensor), a focus detection device (anautomatic focus (AF) sensor), and a photometric device (an automaticexposure (AE) sensor). The photoelectric conversion device 1 can have aplurality of sensor functions and be configured as, for example, animaging device capable of detecting a focus by an imaging plane phasedifference method. An imaging system can be constituted using thephotoelectric conversion device. The imaging system is an informationterminal including a camera and an imaging function. The imaging systemcan include a signal processing device for processing a signal obtainedfrom the photoelectric conversion device and a display device fordisplaying an image captured by the photoelectric conversion device.

Next, a configuration of the photoelectric conversion device accordingto a first exemplary embodiment is described below with reference toFIGS. 2A to 2C.

FIG. 2A illustrates an example of a circuit configuration of the pixelcircuit 2. The pixel circuit 2 can include a photoelectric conversionelement 10 such as a photodiode, a transfer transistor 11, a floatingnode 12, an amplification transistor 13, a reset transistor 14, and aselection transistor 15. A transfer signal TX is applied to a gateterminal of the transfer transistor 11 via the transfer signal line 20.When the transfer signal TX is activated, a charge generated byphotoelectric conversion in the photoelectric conversion element 10 istransferred to the floating node 12 by the transfer transistor 11. Thefloating node 12 is connected to a gate terminal of the amplificationtransistor 13, and a source potential of the amplification transistor 13changes according to variation in a charge amount transferred to thefloating node 12. The amplification transistor 13 constitutes a sourcefollower in which a source is connected to a current source 26 via theselection transistor 15. A selection signal SEL is applied to a gateterminal of the selection transistor 15 via the selection signal line22. When the selection signal SEL is activated, the selection transistor15 outputs, to the output signal line 23, a signal corresponding to agate potential of the amplification transistor 13 as a signal based on acharge generated by the photoelectric conversion element 10. A resetsignal RES is applied to a gate terminal of the reset transistor 14 viathe reset signal line 21. When the reset signal RES is activated, thereset transistor 14 resets a potential of the floating node 12. Further,the reset transistor 14 can reset the charge of the photoelectricconversion element 10.

FIG. 2B is a plane schematic diagram illustrating a layout example ofthe pixel circuit 2. Diagrams A and B in FIG. 2C are respectivelycross-sectional schematic views of the pixel circuit along a line A-A′and a line B-B′ in FIG. 2B.

A substrate 100 includes a semiconductor region 101 and an insulatorregion 102 on its surface. The semiconductor region 101 includes aplurality of impurity regions distinguished by impurity concentrationsand conductivity types. The insulator region 102 for element isolationhas a local oxidation of silicon (LOCOS) structure and/or a shallowtrench isolation (STI) structure and defines the semiconductor region101. The semiconductor region 101 functions as an active region and anelement region, and the insulator region 102 functions as an inactiveregion and/or an element isolation region. An example in which a singlepixel circuit 2 includes only one semiconductor region 101 is describedhere, however, a single pixel circuit 2 can includes a plurality of thesemiconductor regions 101.

The semiconductor region 101 includes a p-type impurity region 141. Theimpurity region 141 is a well region. The pixel circuit 2 is formed inthe impurity region 141. The photoelectric conversion element 10 in FIG.2A is, for example, an embedded type photodiode and includes an n-typeimpurity region 142 which accumulates an electron as a signal charge. Ap-type impurity region 143 is disposed between the impurity region 142and a surface of the semiconductor region 101. The photoelectricconversion element 10 includes a depletion region. The depletion regionis formed by the impurity region 142 and the impurity regions (theimpurity regions 141, 143, and the like) forming a pn junction with theimpurity region 142. The floating node 12 in FIG. 2A includes an n-typeimpurity region 144 to which a signal charge is transferred. Theimpurity region 144 is a floating diffusion region. The amplificationtransistor 13, the reset transistor 14, and the selection transistor 15in FIG. 2A each includes an n-type impurity region 145. The impurityregion 145 is a source-drain region. The source-drain region means animpurity region corresponding to at least one of a source and a drain ofa transistor. Depending on a driving state and a layout, the sameimpurity region can be a source and a drain of the same transistor ordifferent transistors. In the present example, a drain of the transfertransistor 11 is also a source of the reset transistor 14, and a drainof the amplification transistor 13 is also a drain of the resettransistor 14. In addition, the impurity region 142 of the photoelectricconversion element 10 is also a source of the transfer transistor 11.

As illustrated in FIGS. 2B and 2C, a plurality of gate electrodes isdisposed on the semiconductor region 101 via a gate insulating film. Thetransfer transistor 11 in FIG. 2A includes a gate electrode 111, and thereset transistor 14 in FIG. 2A includes a gate electrode 112. Theamplification transistor 13 in FIG. 2A includes a gate electrode 113,and the selection transistor 15 in FIG. 2A includes a gate electrode114. At least a portion of each of the gate electrodes 111, 112, 113,and 114 is located above the semiconductor region 101 via the gateinsulating film. Accordingly, portions located below the gate electrodes111, 112, 113, and 114 of the semiconductor region 101 function aschannel regions in which channels are formed. In the present example, aportion of each of the gate electrodes 111, 112, 113, and 114 is locatedabove the insulator region 102 as the element isolation region. Aninsulator constituting the insulator region 102 suppresses generation ofa parasitic channel below the gate electrode. An entire portion of eachof the gate electrodes 111, 112, 113, and 114 may be located above thesemiconductor region 101. In such a case, a portion of each of the gateelectrodes 111, 112, 113, and 114 can be located above the channelregion and a remaining portion thereof can be located above the elementisolation region having a pn junction isolation structure. Each gateelectrode contains, for example, silicon, germanium, or a mixture ofsilicon and germanium, and typically a polycrystalline material of theseelements. A thickness of each gate electrode is, for example, 50 nm ormore and 500 nm or less. The present exemplary embodiment is suitablefor a case in which a thickness of each gate electrode is 100 nm or moreand 400 nm or less, and especially a case of 200 nm or less. Each gateelectrode may have a polycide structure including a polysilicon layerand a silicide.

An insulator member 151 covering the plurality of gate electrodes isdisposed on the substrate 100. The insulator member 151 may be alaminated member including a plurality of insulator layers. Theinsulator member 151 includes a plurality of holes (contact holes).

A plurality of plugs (gate plugs) is disposed on the substrate 100 as aconductor member being in contact with the gate electrode. For example,there are a plug 121 being in contact with the gate electrode 111, aplug 123 being in contact with the gate electrode 112, a plug 125 beingin contact with the gate electrode 113, and a plug 126 being in contactwith the gate electrode 114. Further, a plurality of plugs (contactplugs) is disposed on the substrate 100 as a conductor member being incontact with the semiconductor region 101. For example, there are a plug122 being in contact with the drain of the transfer transistor 11 inFIG. 2A, a plug 124 being in contact with the drain of the amplificationtransistor 13 in FIG. 2A, and a plug 127 being in contact with a sourceof the selection transistor 15. Each plug can include, for example, aconductive portion containing tungsten as a main component and a barriermetal portion containing titanium and titanium nitride as maincomponents.

Wirings connected to the gate plugs and the contact plugs are disposedon the insulator member 151. The wirings include global wirings, such asthe signal lines 20, 21, 22, and 23 and the power source line 19 andalso a local wiring 16 (see FIG. 2C). The local wiring 16 connects theimpurity region 144 with the gate electrode 113 and can be a part of thefloating node 12. Each wiring can include a conductive portioncontaining aluminum and copper as main components and a barrier metalportion containing titanium, titanium nitride, tantalum, and tantalumnitride as main components. The wirings are formed by a plurality ofwiring layers. An insulator member 152 insulates between wirings in thesame wiring layer and between different wiring layers.

The gate plugs and the contact plugs as conductor members are in contactwith the gate electrode and the semiconductor region through holes ofthe above-described insulator member 151. The gate plugs and the contactplugs are disposed only inside of the holes of the insulator member 151.In this case, a conductor member being in contact with the gateelectrode or the semiconductor region can be made of a materialdifferent from a wiring disposed outside of the hole of the insulatormember 151.

The plugs 122, 124, and 127 (contact plugs) being in contact with thesemiconductor region 101 are inevitably located above the semiconductorregion 101. However, the plugs 121, 123, 125, and 126 (gate plugs) beingin contact with the gate electrodes can be located above thesemiconductor region 101 or above the insulator region 102.

Among a plurality of the gate plugs, for example, the plug 125 islocated above the insulator region 102. In other words, the plug 125 isin contact with a portion located above the insulator region 102 of thegate electrode 113.

If a plug exists above the channel region in the transistor, it may be acause of noise. For example, in the amplification transistor 13 (seeFIG. 2A) for generating a signal, noise generated in the channel regionis likely to be a cause of fixed pattern noise. According to the presentexemplary embodiment, the plug 125 connected to the gate electrode 113of the amplification transistor is disposed on the insulator region 102and thus noise can be suppressed.

On the other hand, among the plurality of the gate plugs, for example,the plugs 121, 123, and 126 are located above the semiconductor region101. Further, the plugs 121, 123, and 126 are respectively in contactwith portions located above the semiconductor region 101 in the gateelectrodes 111, 112, and 114.

An effect of noise in the channel region is small in the resettransistor and the selection transistor having a switch function ofmainly switching ON and OFF, so that the plugs 121, 123, and 126 arelocated above the semiconductor region 101. Accordingly, areas ofportions located above the insulator regions 102 of the correspondinggate electrodes 112 and 114 are reduced, and the pixel circuit 2 can beminiaturized.

In the present example, the plug 121 of the transfer transistor forhandling a signal charge is located above the semiconductor region 101,however, the plug 121 may be located above the insulator region 102 tosuppress noise such as a dark current.

The gate electrode 113 includes a high concentration portion 154 ofwhich impurity concentration is higher than another portion (a lowconcentration portion) in the gate electrode 113. Accordingly,resistance of the gate electrode 113 becomes low, and if the plug 125 isdisposed on the insulator region 102, the gate electrode 113 can operateat high speed. The plug 125 can be in contact with the highconcentration portion 154. A net conductivity type (“net” is theopposite of “gross”) of the high concentration portion 154 is the sameas the conductivity type (n-type) of the transistor including the gateelectrode 113. However, if resistance between the gate electrode 113 andthe plug 125 can be lowered, an impurity having a conductivity type(p-type) opposite to that of the transistor including the gate electrode113 can be introduced to the high concentration portion 154.

In contrast, the impurity concentrations of the gate electrodes 111,112, and 114 are entirely on the same level as that the lowconcentration portion of the gate electrode 113. In other words, thewhole of the gate electrodes 111, 112, and 114 are the low concentrationportions. The plugs 121, 123, and 126 are in contact with the lowconcentration portions. Accordingly, the impurity concentration of aportion (the high concentration portion 154) being in contact with theplug 125 of the gate electrode 113 is higher than the impurityconcentrations of portions (the low concentration portions) being incontact with the plugs 121, 123, and 126 of the gate electrodes 111,112, and 114. The impurity concentration of the entire gate electrode113 may be set higher than the impurity concentrations of the gateelectrodes 111, 112, and 114.

Next, a first example of a manufacturing method of the photoelectricconversion device according to the first exemplary embodiment isdescribed with reference to FIGS. 3A to 3D.

First, the insulator region 102 having an element isolation structuresuch as a LOCOS structure and a STI structure is formed on, for example,a p-type silicon substrate. Accordingly, as illustrated in FIG. 3A, aregion is separated to the semiconductor region 101 including the p-typeimpurity region 141 and the insulator region 102. Next, the gateinsulating film 109 is formed, and then a conductor film 110 is formedon the gate insulating film 109. The conductor film 110 may be made of asemiconductor material including an impurity. Silicon, germanium, or amixture of silicon and germanium is appropriate for the semiconductormaterial.

The conductor film 110 containing the impurity can be formed by a firstmethod as described below. For example, an amorphous film of thesemiconductor is formed on the substrate 100 by a chemical vapordeposition method. For the amorphous film, an amorphous silicon film isappropriate of which a film thickness is 100 to 300 nm (for example, 150nm). More specifically, an amorphous silicon film can be formed in anatmosphere of a silane based gas (for example, SiH₄) under conditions of500 to 650° C. (for example, 580° C.) in a reaction temperature and 15to 60 Pa (for example, 30 Pa) in a gas pressure.

Then, an impurity is introduced to the amorphous film by ionimplantation and the like. The amorphous film is polycrystallized asnecessary. For example, phosphorus ions are introduced to the amorphoussilicon film in a dose amount of 1*10¹⁵ ions/cm² and at an acceleratingvoltage 20 keV. Further, the amorphous silicon film is annealed in anitrogen atmosphere at 600° C. for 60 seconds, so that a polysiliconfilm containing the impurity can be formed. At that time, it isdesirable that energy of the ion implantation is set so that a sum of arange distance Rp and six times a standard deviation of the range ΔRp(i.e., Rp+6ΔRp) is smaller than a film thickness of the gate electrode.

In addition, the conductor film 110 containing the impurity can beformed by a second method as described below. For example, apolycrystalline film is formed on the substrate 100 using a gascontaining the impurity by the chemical vapor deposition method. For thepolycrystalline film, an amorphous silicon film is appropriate of whicha film thickness is 300 to 500 nm (for example, 400 nm). Morespecifically, a polysilicon film including phosphorus as the impuritycan be formed in an atmosphere of a mixed gas of SiH₄ and PH₃ underconditions of 500 to 650° C. (for example, 540° C.) in a reactiontemperature and 30 to 100 Pa (for example, 70 Pa) in a gas pressure. Atthat time, it is desirable that the impurity concentration near asurface of the gate electrode is 1*10¹⁷ atoms/cm³ or more. According tothe present exemplary embodiment, polarity of the gate electrode isdescribed as an n-type as an example, however, polarity of all or a partof the gate electrodes can be a p-type opposite to the n-type. In such acase, it is desirable that the impurity concentration near the surfaceof the gate electrode is 2*10¹⁷ atoms/cm³ or more.

Next, the conductor film 110 is subjected to patterning usingphotolithography. Accordingly, as illustrated in FIG. 3B, the gateelectrode 111 of the transfer transistor, the gate electrode 112 of thereset transistor, the gate electrode 113 of the amplificationtransistor, and the gate electrode 114 of the selection transistor areformed.

After the patterning of the gate electrode, the n-type impurity region142, the p-type impurity region 143, and the n-type impurity region 144are formed by, for example, ion implantation. The n-type impurity region142, the p-type impurity region 143, and the n-type impurity region 144can be formed before the film formation of the gate electrode. It isdesirable that a surface concentration of the n-type impurity region 144is set to 5*10¹⁶ atoms/cm³ or less from viewpoints of reduction incapacity of the floating node 12, hot carrier resistance of the MOStransistor of the pixel circuit 2, and the like. When the impurityregions 142, 143, and 144 are formed after the patterning of the gateelectrode, it is desirable to mask the gate electrode with photoresistand the like so that an unnecessary impurity is not introduced to thegate electrode.

Next, an insulator film is formed on the substrate 100. The insulatorfilm is subjected to planarization processing by chemical mechanicalpolishing (CMP), etch back, reflow, and the like, as necessary. Then, aplurality of holes to be the contact holes is formed on the insulatorfilm using the photolithography. The plurality of holes as the contactholes includes holes 161, 163, and 166 to which the plugs 121, 123, and126 are provided later. The plurality of holes includes a hole 165 towhich the plug 125 is provided later. The plurality of holes includesholes 162, 164, and 167 to which the plugs 122, 124, and 127 areprovided later. Accordingly, as illustrated in FIG. 3C, the insulatormember 151 including the plurality of holes is formed from theabove-described insulator film. Then, a photosensitive resin film (aphotoresist film) is formed on the insulator member 151, and thephotosensitive resin film is subjected to patterning using thephotolithography. Accordingly, a resin made mask 171 is formed from thephotosensitive resin film. The mask 171 covers the holes 161, 163, and166 among the plurality of holes. On the other hand, the mask 171 doesnot cover the holes 162, 164, 165, and 167 among the plurality of holesbecause of openings 131, 132, and 133 disposed on the mask 171.

The impurity is selectively introduced to at least a portioncorresponding to a hole disposed on the insulator member 151 in thesemiconductor region 101 in the MOS transistor of the pixel circuit 2through the openings 131, 132, and 133 of the mask 171 and the holes162, 164, and 167. According to the present exemplary embodiment, ionimplantation is performed on a source-drain region on which the openings131, 132, and 133 are disposed and further the holes 162, 164, 165, and167 are formed. At the same time, the impurity is selectively introducedto a portion corresponding to the hole 165 of the gate electrode 113through the opening 132 of the mask 171 and the hole 165. It isdesirable that a conductivity type of the impurity implanted in thepresent process is the same as a conductivity type (n-type) of thesource-drain region, however, an impurity having a conductivity type(p-type) opposite to the source-drain region may be introduced in aregion in which the gate electrode 113 can be conducted to a conductormember.

Then, the anneal processing is appropriately performed, and thus acontact region 153 of which an impurity concentration is higher than theother portions of the source-drain region is formed in the source-drainregion. In addition, the high concentration portion 154 of which theimpurity concentration is higher than the other portions is formed onthe gate electrode 113. Conditions of ion implantation performed whenthe source-drain region is formed is referred to as a first dose amountand a first implantation energy. When the contact region 153 is formed,the ion implantation can be adopted which uses a second dose amounthigher than the first dose amount and a second implantation energy lowerthan the first implantation energy. The ion implantation in thesource-drain region can be performed under the conditions that a dose is10¹³ ions/cm² or more and 10¹⁵ ions/cm² or less, and an acceleratingvoltage is 10 keV or more and 40 keV or less. For example, a dose amountof phosphorus ions is set to 1*10¹⁴ ions/cm² and an accelerating voltageis set to 20 keV. For example, the impurity concentration of the contactregion 153 disposed on the impurity region 144 is desirably 1*10¹⁷atoms/cm³ or more.

According to the present exemplary embodiment, n-type chargeaccumulation regions and n-type MOS transistors are described asexamples, however, a p-type MOS transistor having an opposite polaritycan be adopted. In such a case, the impurity concentration of thecontact region 153 is desirably 2*10¹⁷ atoms/cm³ or more.

Next, after removing the photoresist, for example, a titanium (Ti) layerwith about 10 nm in thickness, a titanium nitride (TiN) layer with about30 nm in thickness are formed as barrier metal portions of the plugs 121to 127, and, for example, a tungsten layer with about 200 nm inthickness is formed as conductive portions of the plugs 121 to 127.Then, extra tungsten and barrier metal portions are removed by CMP orthe like, and thus, as illustrated in FIG. 3D, the conductor member isembedded in the contact hole. The barrier metal portions may includetantalum (Ta), tantalum nitride (TaN), and others as well. Then, wiringsconnected to each of plugs are appropriately formed. Further, apassivation film, a color filter array, and a microlens array areformed, so that the photoelectric conversion device is completed. InFIG. 2B, a section in which a single color filter in the color filterarray or a single microlens in the microlens array is disposed isindicated as a section P. The section P can be handled as a pixel.

According to the present exemplary embodiment, the plugs 121, 123, and126 being in contact with the gate electrode 111 of the transfertransistor, the gate electrode 112 of the reset transistor, and the gateelectrode 114 of the selection transistor are formed above thesemiconductor region 101 (above the channel region). In contrast, theplug 125 being in contact with the gate electrode 113 of theamplification transistor is formed above the insulator region 102.Further, according to the present exemplary embodiment, the impurityconcentration of the portion to which the plug 125 of the gate electrode113 is connected is higher than the impurity concentration of theportion to which a plug of another gate electrode is connected. This isbecause the ion implantation is selectively performed by the openings131, 132, and 133.

A reason why the ion implantation is not performed on a portion locatedabove the semiconductor region 101 (the channel region) of the gateelectrode is described below. If the ion implantation is performed onthe gate electrode made of a polycrystallized semiconductor material,there is a possibility to cause a sub-channeling phenomenon andpenetration of a void at a grain boundary portion. It is difficult toprevent such phenomena from occurring by ion implantation angle control,such as interstitial channeling and lattice scattering. Therefore, theimpurity may penetrate through the gate electrode and reach the gateinsulating film and the semiconductor substrate therebelow. Especially,in a case where a region to which the impurity is implanted is locatedabove the channel region of the semiconductor region 101, and if theimpurity is unintentionally introduced to the channel region, athreshold value of a transistor is shifted, and deterioration ofcharacteristics and a malfunction may occur in the photoelectricconversion device. According to the present exemplary embodiment, in thegate electrode 113, the impurity is introduced to a portion locatedabove the insulator region 102 to form the high concentration portion154, and the plug 125 is in contact with the high concentration portion154. The portion to which the impurity is introduced (the highconcentration portion 154) of the gate electrode 113 is formed on theinsulator region 102 made of a thick insulator (the STI in the example).Therefore, there is no effect if the implanted impurity penetratesthrough the gate electrode 113. Further, disposing the highconcentration portion 154 makes resistance to the plug 125 smaller andenables a high speed operation.

On the other hand, the holes 161, 163, and 166 on the gate electrodes111, 112, and 114 are formed above the channel region of thesemiconductor region 101. The gate electrodes 111, 112, and 114 are incontact with the plugs 121, 123, and 126 at portions located above thesemiconductor region 101. Thus, a degree of freedom for a layout of theMOS transistor for the pixel circuit can be improved. The holes 161,163, and 166 on which the plugs 121, 123, and 126 are disposed arecovered by the mask 171, so that the impurity is not casually introducedto the channel region below the holes 161, 163, and 166. Accordingly,characteristics of the pixel circuit can be optimized. Regardingconnections between the plugs 121, 123, and 126 and the gate electrodes111, 112, and 114, the conductor film 110 for forming the gateelectrodes 111, 112, and 114 contains the impurity, so that resistanceof the gate electrodes 111, 112, and 114 are low in advance. Therefore,the gate electrodes 111, 112, and 114 can ensure sufficiently highconductivity without disposing the high concentration portion. Regardingthe formation of the conductor film 110, in the first method,introduction of the impurity to the conductor film (the gate electrode)is performed by the ion implantation not in the polycrystalline film butin the amorphous film.

Accordingly, penetration of ions through the conductor film (the gateelectrode) can be suppressed compared to the case that the ionimplantation is performed on the polycrystalline film. In the secondmethod, introduction of the impurity to the conductor film (the gateelectrode) is performed not in the ion implantation but in the filmformation. Therefore, unnecessary introduction of the impurity to thesemiconductor region 101 can be suppressed.

Next, a second example of the manufacturing method of the photoelectricconversion device according to the first exemplary embodiment isdescribed with reference to FIGS. 5A and 5B. FIGS. 5A and 5B partiallyillustrate the manufacturing method different from the first example.Diagrams A and B in FIG. 5A are respectively cross-sectional schematicviews of the pixel circuit along the line A-A′ and the line B-B′ in FIG.2B.

Before the insulator member 151 and the holes 161 to 167 are formed, thephotosensitive resin film (the photoresist film) is formed on thesubstrate 100, and the photosensitive resin film is subjected topatterning using the photolithography. Accordingly, a resin made mask172 is formed from the photosensitive resin film. Openings 134, 135, and136 are disposed on the mask 172. The impurity is introduced to thesemiconductor region 101 and the gate electrode 113 by the ionimplantation through the openings 134, 135, and 136. The ionimplantation is performed only on a region in which the openings 134,135, and 136 of the mask 172 are opened. Then, the anneal processing isappropriately performed, and thus the contact region 153 and the highconcentration portion 154 are formed.

Then, an insulator film 150 covering the contact region 153 and the highconcentration portion 154 is formed. The planarization processing isperformed on the insulator film 150 to a position indicated by a dottedline in FIG. 5B. Then, holes for exposing the contact region 153, thehigh concentration portion 154, or the gate electrodes 111, 112, and114, where the contact region 153 and the high concentration portion 154are not formed, are formed on the insulator film 150 after theplanarization processing similar to the holes 161 to 167 in FIG. 3C.Accordingly, the insulator member 151 including the holes 161 to 167 isformed similar to the first example. Then, as similar in FIG. 3D, theplugs 121 to 127 are formed which are in contact with the contact region153, the high concentration portion 154, or the gate electrodes 111,112, and 114, where the contact region 153 and the high concentrationportion 154 are not formed, through the holes 161 to 167. As in thepresent example, the contact region 153 and the high concentrationportion 154 can be formed before the formation of the insulator member151 as long as it is after the patterning of the gate electrode.

Next, a configuration of a photoelectric conversion device according toa second exemplary embodiment is described with reference to FIG. 4A to4C.

FIG. 4A illustrates an example of the circuit configuration of the pixelcircuit 2. Diagrams C, D, and E in FIG. 4C are respectivelycross-sectional schematic views of the pixel circuit along a line C-C′,a line D-D′, and a line E-E′ in FIG. 4B. A diagram F in FIG. 4C is across-sectional schematic view of the MOS transistor 15 included inportions other than the pixel unit 18 in FIG. 1, namely peripheralcircuits such as the driving unit 24, the signal processing unit 25, thecontrol unit 27, and the output unit 29. Descriptions of points whichare not different from those in the first exemplary embodiment areomitted by assigning the same reference numerals or common referencenumerals except attached alphabets used in the first exemplaryembodiment.

According to the present exemplary embodiment, an example of a circuitconfiguration of the pixel circuit is described in which a plurality ofphotoelectric conversion elements 10 a and 10 b and transfer transistors11 a and 11 b share an amplification transistor 13 and a resettransistor 14. In addition, a selection transistor and a selectionsignal line 22 are not included in the circuit configuration example. InFIGS. 3A to 3D, two photoelectric conversion elements 10 a and 10 bshare the amplification transistor 13 and the reset transistor 14,however, the present exemplary embodiment is not limited to this circuitconfiguration, and three or more photoelectric conversion elements 10may share them.

The semiconductor region 101 includes a first element region 101 a, asecond element region 101 b, and a third element region 101 c defined bythe insulator region 102 as the element isolation region. The firstelement region 101 a includes the photoelectric conversion element 10 aand the transfer transistor 11 a. The second element region 101 bincludes the photoelectric conversion element 10 b, the transfertransistor 11 b, and the reset transistor 14. The third element region101 c includes the amplification transistor 13.

A plug 121 a is disposed to each of the transfer transistors 11 a and 11b and gate electrodes 111 a and 111 b. The gate electrode 113 of theamplification transistor 13 is extended on the semiconductor region 101,specifically from the channel region of the second element region 101 bto the insulator region 102. The gate electrode 113 is connected to thesemiconductor region 101, specifically to impurity regions 144 a and 144b by respective plugs 120 a and 120 b. The plug 120 a is in contact withboth of the gate electrode 113 and the impurity region 144 a of thesemiconductor region 101, and the plug 120 b is in contact with both ofthe gate electrode 113 and the impurity region 144 b of thesemiconductor region 101. As described above, according to the presentexemplary embodiment, the plugs 120 a and 120 b as conductor membershave a shared contact structure. A plug 128 connected to the outputsignal line is in contact with a source of the amplification transistor13 not via the selection transistor. The impurity regions 144 a, 144 b,and 145 include the contact region 153 which is the high concentrationportion. The gate electrode 113 also includes the high concentrationportion 154. The plugs 120 a and 120 b are in contact with the contactregion 153 and the high concentration portion 154. In the presentexample, portions with which the plugs 120 a and 120 b of the gateelectrode 113 are in contact are located above the insulator region 102.However, the portions with which the plugs 120 a and 120 b of the gateelectrode 113 are in contact may be located above the semiconductorregion 101 or above the both of the semiconductor region 101 and theinsulator region 102.

A plug 129 is in contact with a drain of the reset transistor 14.Wirings such as the power source line 19 and the signal lines 20 to 23connected to each of the plugs 120 to 129 contain, for example, copperas a main component.

The MOS transistor 15 is, for example, a positive channel metal oxidesemiconductor (PMOS) transistor or a negative channel metal oxidesemiconductor (NMOS) transistor constituting a complementary metal oxidesemiconductor (CMOS) circuit. The MOS transistor 15 having a lightlydoped drain (LDD) structure includes a source-drain region including theimpurity region 146 with a low impurity concentration and the impurityregion 147 with a high impurity concentration. The impurityconcentration of the impurity region 147 may be higher than the impurityconcentrations of the impurity regions 144 and 145. A silicide layer 155of cobalt silicide, molybdenum silicide, and the like is disposed on theimpurity region 147 of the MOS transistor 15, and a plug 157 is incontact with the silicide layer 155. A silicide layer 156 of cobaltsilicide, molybdenum silicide, and the like is disposed on a gateelectrode 115 of the MOS transistor 15, and a plug 158 is in contactwith the silicide layer 156.

In FIG. 4B, a section in which a single color filter in the color filterarray or a single microlens in the microlens array is disposed isindicated as a section P1 or P2. Each of the sections P1 and P2 can behandled as a pixel.

Next, a first example of the manufacturing method of the photoelectricconversion device according to the second exemplary embodiment isdescribed with reference to FIG. 5C. FIG. 5C partially illustrates amanufacturing process different from the first example of themanufacturing method according to the first exemplary embodiment.Diagrams C, D, and E in FIG. 5C are respectively cross-sectionalschematic views of the pixel circuit along a line C-C′, a line D-D′, anda line E-E′ in FIG. 3B.

According to the second exemplary embodiment, the same processesaccording to the first exemplary embodiment are adopted up to theprocesses illustrated in FIG. 3B except for a difference in a layout ofthe circuit.

After the processes illustrated in FIG. 3B, the impurity region 146 ofthe MOS transistor 15 (see FIG. 4C) included in the peripheral circuitis formed. Further, a sidewall spacer is formed on a side surface of thegate electrode 115, and the impurity region 147 is formed with a dosehigher than that of the formation of the impurity region 146. Theimpurity region 147 is formed, for example, by the ion implantation andthe anneal processing at 600° C. or higher.

Further, the MOS transistor 15 is subjected to silicidation. At thattime, a salicide process can be adopted which protects the transistor ofthe pixel unit 18 from silicidation by a protective film (a silicideblock film). Accordingly, as described with reference to FIG. 4C, thesilicide layer 155 is formed on the source-drain region of the MOStransistor 15 in the peripheral circuit, and the silicide layer 156 isformed on a surface of the gate electrode 115.

Next, as illustrated in FIG. 5C, an insulator member 251 including aplurality of holes is formed. The insulator member 251 includes holes168 and 169 above the semiconductor region 101. Further, the insulatormember 251 respectively includes holes 161 a and 163 on the gateelectrodes 111 a and 112. Furthermore, the insulator member 251 includesa hole 160 a above the semiconductor region 101 and on the gateelectrode 113. Next, a mask 271 is formed similar to that in the firstexample of the manufacturing method according to the first exemplaryembodiment. The mask 271 covers the holes 161 a and 163. On the otherhand, since openings 231, 232, and 233 are disposed on the mask 271, themask 271 does not cover the holes 160 a, 168, and 169 among theplurality of holes. The impurity is introduced to the impurity region145 of the semiconductor region 101 by the ion implantation through theopenings 232 and 233 and the holes 168 and 169 to form the contactregion 153. In addition, the impurity is introduced to the impurityregion 144 a by the ion implantation through the opening 231 and thehole 160 a to form the contact region 153, and the impurity isintroduced to the gate electrode 113 a to form the high concentrationportion 154. A portion located on the gate electrode 113 a of the hole160 a may be located only above the insulator region 102, only above thesemiconductor region 101 a, or above both of the semiconductor region101 and the insulator region 102. A reason why the hole 160 a may belocated above the semiconductor region 101 is that the semiconductorregion 101 below the hole 160 a is not the channel region but thesource-drain region or a region which does not substantially affect anoperation of the transistor. A portion of the impurity introduced to thegate electrode 113 a to form the high concentration portion 154 may beintroduced to the semiconductor region 101 by penetrating through thegate electrode 113 a. However, if the impurity is introduced to a regionother than the channel region of the transfer transistor 11 a, effectson a threshold value and transfer characteristics are small compared tothe case that the impurity is introduced to the channel region.

Next, a plurality of plugs including the plugs 120 a and 120 billustrated in FIG. 4C is formed. In addition, wirings connected to theplurality of plugs are formed. A damascene process can be adopted toformation of wirings mainly containing copper. A silicide layer (notillustrated) may be formed between the contact region 153 and the highconcentration portion 154 after the plurality of plugs is formed in thepixel region. The silicide layer is formed by reaction of tungstenand/or titanium contained in the plugs 121 to 127 themselves and siliconcontained in the substrate and the gate electrodes 111 to 114. Thesilicide layer formed on the MOS transistor of the pixel circuit can beformed later than the above-described salicide process performed on theMOS transistor of the peripheral circuit. As described above, a metalliccomponent of the silicide layer formed on the MOS transistor of thepixel circuit accompanying the formation of the plugs 121 to 127 may bedifferent from that of the silicide layers 155 and 156. For example,tungsten silicide and titanium silicide are formed on the MOS transistorof the pixel circuit, whereas cobalt silicide and nickel silicide can beformed on the MOS transistor of the peripheral circuit. A fact that thegate electrodes 111 to 114 include the silicide layers below the plugs121 to 127 is advantageous for the MOS transistor of the pixel circuitin reduction of resistance between the gate electrodes 111 to 114 andthe plugs 121 to 127.

A second example of the manufacturing method of the photoelectricconversion device according to the second exemplary embodiment isperformed similar to the second example of the manufacturing method ofthe photoelectric conversion device according the first exemplaryembodiment. More specifically, as illustrated in FIG. 5D, before formingthe insulator member 151, a mask 272 is formed which is obtained byperforming patterning on the photosensitive resin film. Openings 234 and235 are disposed on the mask 272. The impurity is introduced to theimpurity region 145 by the ion implantation through the opening 235 toform the contact region 153. In addition, the impurity is introduced tothe impurity region 144 a by the ion implantation through the opening234 to form the contact region 153, and the impurity is introduced tothe gate electrode 113 a to form the high concentration portion 154.

A third example of the manufacturing method of the photoelectricconversion device according to the second exemplary embodiment isdescribed with reference to FIG. 5C. After the formation of theinsulator film 150 and planarization, the holes 160 a, 168, and 169 areformed without forming the holes 161 a and 163. Then, the impurity isintroduced to the gate electrode 113 and the impurity regions 153 and145 through the holes 160 a, 168, and 169. Accordingly, the contactregion 153 and the high concentration portion 154 are formed. At thattime, the gate electrodes 111 a and 112 are covered by the insulatorfilm 150 without the holes 161 a and 163, the insulator film 150 servesas a mask to prevent the impurity from being introduced to the gateelectrodes 111 a and 112. Then, the holes 161 a and 163 are formed, sothat the plugs 121 a and 123 can be formed without introducing theimpurity through the holes 161 a and 163. The plugs 120 a, 128, and 129may be formed to the holes 160 a, 168, and 169 after the formation ofthe holes 161 a and 163. When the holes 161 a and 163 are formed beforethe formation of the holes 160 a, 168, and 169, the holes 161 a and 163may be covered by the resist as in the first example of the secondexemplary embodiment.

Accordingly, the above-described exemplary embodiments can provide atechnique advantageous for improving performance of a photoelectricconversion circuit. The above-described exemplary embodiments can beappropriately modified without departing from the technical ideathereof.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2014-222044, filed Oct. 30, 2014, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A manufacturing method of a photoelectricconversion device in which a pixel circuit including a metal oxidesemiconductor (MOS) transistor is arranged, the manufacturing methodcomprising: a first process for forming a gate electrode and asource-drain region of the MOS transistor; a second process for maskinga first portion in the gate electrode, the first portion beingconstituted by polysilicon and located above a channel region of the MOStransistor, and introducing an impurity having a conductivity type sameas that of the source-drain region to a second portion located in thesource-drain region; and a third process for forming a conductor memberbeing in contact with the first portion through a first hole disposed onan insulator member covering the MOS transistor and a conductor memberbeing in contact with the second portion through a second hole disposedon the insulator member.
 2. The manufacturing method of thephotoelectric conversion device according to claim 1, wherein, the gateelectrode including the first portion is regarded as a first gateelectrode, the MOS transistor including the first gate electrode isregarded as a first MOS transistor, and the pixel circuit furtherincludes a second MOS transistor including a second gate electrode, inthe first process, the second gate electrode is formed, in the secondprocess, an impurity is introduced to the second gate electrode bymasking the first portion, and in the third process, a conductor memberis formed which is in contact with the second gate electrode through athird hole disposed on the insulator member.
 3. The manufacturing methodof the photoelectric conversion device according to claim 2, wherein, inthe third process, the conductor member being in contact with the secondgate electrode is in contact with a portion to which the impurity isintroduced in the second gate electrode and a semiconductor regiondifferent from a semiconductor region of the second MOS transistor. 4.The manufacturing method of the photoelectric conversion deviceaccording to claim 2, wherein, in the first process, the second gateelectrode is formed in such a manner that the second gate electrodeincludes a third portion located above an insulator region for elementisolation, in the second process, an impurity is introduced to the thirdportion by masking the first portion, and in the third process, theconductor member being in contact with the second gate electrode is incontact with the third portion.
 5. The manufacturing method of thephotoelectric conversion device according to claim 1, wherein theinsulator member is formed before the second process, and in the secondprocess, an impurity is introduced to the second portion through thesecond hole disposed on the insulator member.
 6. A manufacturing methodof a photoelectric conversion device in which a pixel circuit includinga MOS transistor is arranged, the manufacturing method comprising: afirst process for forming an insulator film covering a gate electrodeand a source-drain region of the MOS transistor and etching theinsulator film to form an insulator member including a first hole on afirst portion located above a channel region of the MOS transistor inthe gate electrode and a second hole on a second portion located in thesource-drain region; a second process for forming a mask covering thefirst hole after forming the first hole and the second hole andintroducing an impurity having a conductivity type same as that of thesource-drain region to a second portion located in the source-drainregion in a state in which the first hole is covered by the mask; and athird process for forming a conductor member being in contact with thefirst portion through the first hole and a conductor member being incontact with the second portion through the second hole.
 7. Themanufacturing method of the photoelectric conversion device according toclaim 1, wherein the insulator member is formed after the secondprocess, and in the second process, an impurity is introduced to thesecond portion through an opening disposed on a resin film covering thefirst portion.
 8. The manufacturing method of the photoelectricconversion device according to claim 1, wherein, in the first process, aconductor film containing an impurity is formed, and then the gateelectrode including the first portion is formed by performing patterningon the conductor film.
 9. The manufacturing method of the photoelectricconversion device according to claim 8, wherein, in the first process,the conductor film is formed using a gas including the impuritycontained in the conductor film, or in the first process, an amorphousfilm is formed, and the conductor film is formed by introducing animpurity to the amorphous film.
 10. The manufacturing method of thephotoelectric conversion device according to claim 1, wherein, in thefirst process, the source-drain region is formed by introducing animpurity by ion implantation using a first dose amount and a firstimplantation energy, and in the second process, an impurity isintroduced to the second portion by ion implantation using a second doseamount higher than the first dose amount and a second implantationenergy lower than the first implantation energy.
 11. A photoelectricconversion device in which a pixel circuit including a first MOStransistor having a first gate electrode and a second MOS transistorhaving a second gate electrode is arranged, the photoelectric conversiondevice comprising: a first conductor member being in contact with thefirst gate electrode; and a second conductor member being in contactwith the second gate electrode, wherein the first conductor member islocated above a channel region of the first MOS transistor, and animpurity concentration of a portion located below the second conductormember in the second gate electrode is higher than an impurityconcentration of a portion located below the first conductor member inthe first gate electrode.
 12. The photoelectric conversion deviceaccording to claim 11, wherein the second conductor member is locatedabove an element isolation region.
 13. The photoelectric conversiondevice according to claim 11, wherein the second conductor member is incontact with a drain region of the first MOS transistor.
 14. Thephotoelectric conversion device according to claim 11, wherein the firstgate electrode contains at least one of silicon and germanium, athickness of the first gate electrode is 400 nm or less, and a portionof the first gate electrode is located above an element isolation regionhaving a shallow trench isolation (STI) structure.
 15. The photoelectricconversion device according to claim 11 further comprising a signalprocessing unit configured to process a signal generated by the pixelcircuit, wherein the signal processing unit comprises a MOS transistorincluding a silicide layer, and the first gate electrode includes asilicide layer of which a metallic component is different from thesilicide layer below the first conductor member.
 16. The photoelectricconversion device according to claim 11, wherein the first MOStransistor is a reset transistor for resetting a charge generated byphotoelectric conversion.
 17. The photoelectric conversion deviceaccording to claim 11, wherein the second MOS transistor is anamplification transistor for generating a signal based on a chargegenerated by photoelectric conversion.
 18. The photoelectric conversiondevice according to claim 11, wherein the pixel circuit includes a thirdMOS transistor, the photoelectric conversion device comprises a thirdconductor member being in contact with a third gate electrode of thethird MOS transistor, and the third conductor member is located above achannel region of the third MOS transistor.
 19. The photoelectricconversion device according to claim 18, wherein the third MOStransistor is a transfer transistor for transferring a charge generatedby photoelectric conversion.
 20. The photoelectric conversion deviceaccording to claim 11 constituting an imaging system that comprises asignal processing device configured to process a signal obtained fromthe photoelectric conversion device.